Virtual controller of electromechanical characteristics for static power converters

Abstract

The invention relates to a virtual controller of electromechanical characteristics for a static power converter that includes a PLC (23) (power loop controller), which receives, at the input thereof, the power difference (ΔP) between the input power (P_in) (power delivered to the converter by the primary source) and the power delivered to the grid (P_elec) and is able to modify online the parameters of the virtual inertia coefficient and the damping factor as a function of the desired response and of the grid conditions for different frequency ranges.

Description

OBJECT OF THE INVENTION[0001]The present invention relates to a controller of the virtual electromechanical characteristic for static power converters that, connected to the electric grid, allows the control of the power injected thereto. The main application of this invention is distributed generation plants and especially in renewable energy plants such as wind and photovoltaic energy.BACKGROUND OF THE INVENTION[0002]The sources of renewable energy, mainly wind power plants (WIN) and photovoltaic (PH) power plants, have ceased to be a marginal resource in the generation of electricity. The generators of PH plants use power converters to connect to the electric grid. These power converters, also known as inverters, inject current to the voltage of the grid to supply power to the same. In normal operating conditions, the PH inverters inject single-phase o tri-phase sinusoidal currents to the grid, depending on the power range of the generator. Normally, the currents injected to the ...

AI Technical Summary

Benefits of technology

[0027]This controller of the electromechanical characteristics achieves great flexibility in the behavior of the power converter connected to the grid and allows, for example, reducing the inertia at certain moments to facilitate its connection to the grid, or allocating higher inertias in the frequency ranges in which perturbations are desired to be eliminated.

[0028]It should be noted at this point that not all existing techniques to control the active power in the connection to the electric grid of a power converter implement the inertia characteristic. On the other hand, the techniques applying this concept only attempt to faithfully replicate the electromechanical characteristic of the real synchronous generator without applying any type of additional improvement intending to solve the inconveniences inherent to the electromechanical system of the real synchronous generator. Thus, the controller of the electromechanical characteristic object of this invention presents an evident difference with respect to existing techniques, given that it allows optimizing, on line and in an adaptive manner, the virtual inertia coefficient and the damping factor according to the operating conditions of the power converter, such that establishing the capacity presented by the generator to attenuate different power oscillations existing in the grid (inter-plant, inter-area . . . ) and in the primary generation source (mechanical and structural resonances), is possible.

Problems solved by technology

When the grid voltage is affected by a perturbation, such as imbalances, transients, or harmonics, which is usual in electric grids, conventional PH inverters experience problems to remain appropriately synchronized with the grid voltage, which leads to uncontrolled power flows that cause the PH inverter to worsen the situation of the failure of the grid.

With more serious grid perturbations, such as voltage dips, short-circuits, or power oscillations, conventional PH inverters cannot offer an appropriate support to the electric grid to help maintain the generation system active.

In fact, these serious transient perturbations usually cause the disconnection of the grid in the majority of the commercial PH inverters due to the triggering of some of its overcurrent or overvoltage protections.

However, synchronous generators present problems in their dynamic electromechanical response.

The installation of damper windings is the generalized solution at the synchronous machine level, but the damping degree achieved with them is very small.

Another problem related to the electromechanical response of the synchronous generator is the need to maintain synchronism after a grid failure.

Synchronous generators tend to increase their speed during the failure; after the elimination of this failure, the discrepancy existing between the generator and the rest of the grid can render the reestablishment of the synchronous connection impossible.

If a generator has been disconnected and is desired to be reconnected, the synchronization process can be very fragile depending on the weakness of the grid at the coupling point, with the possibility of creating an inadmissible perturbation on the same during the synchronization process.

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